Currently available high-performance fiber-optic gyros (FOG) typically employ lithium niobate modulators. Lithium niobate (LN) is the material of choice for high-bandwidth modulation of the optical phase waveform to allow closed-loop operation of the gyroscope and to enable scale factor nonlinearity on the order of parts per million (ppm) over wide dynamic ranges. It is known that lithium niobate modulators suffer from crystal defects, which produce sensitivities to environment, especially vacuum or other gas exposures. For this reason, some FOG designs employ a hermetic seal with oxygen-based backfill gases to stabilize LN defects that might otherwise be destabilized by vacuum or other gas exposure.
In a vacuum, the uncoordinated sites in the lithium niobate material are not filled, which causes the band gap to drop to a low level that is below the band gap of lithium niobate material in O2. When a LN phase modulator has a low band gap, the modulator has electrical leakage.
Another problem for currently available lithium niobate phase modulators may occur when other components near the lithium niobate phase modulator outgas. Some outgassed species may degrade the LN band gap even further.
Proton exchanged lithium niobate (HN) optical devices used in optical gyroscopes also suffer from performance degradation when a bias voltage is applied to an HN-based optical device, since the bias voltage creates charge carrier migration.